[openmp] Use GCC style intrinsics for atomics on Clang-cl on aarch64 too

[mstorsjo]

Summary

This fixes compilation in the Clang-cl configuration on aarch64;
Clang doesn't implement all the aarch64 MSVC atomic intrinsics yet.

[DavidSpickett]

Can you explain the structure of the existing #ifdef? I'm having trouble following it.

I think the idea is that gcc on AArch64 would end up in the following #elif (KMP_ASM_INTRINS && KMP_OS_UNIX) || !(KMP_ARCH_X86 || KMP_ARCH_X86_64). On Windows, you'd fall down into the #else. But what each of those blocks includes I'm not sure.

[mstorsjo]

In D138737#3952929, @DavidSpickett wrote:

Can you explain the structure of the existing #ifdef? I'm having trouble following it.

I think the idea is that gcc on AArch64 would end up in the following #elif (KMP_ASM_INTRINS && KMP_OS_UNIX) || !(KMP_ARCH_X86 || KMP_ARCH_X86_64). On Windows, you'd fall down into the #else. But what each of those blocks includes I'm not sure.

As far as I can see, the high level structure right now is this:

#if KMP_ASM_INTRINS && KMP_OS_WINDOWS && !((KMP_ARCH_AARCH64 || KMP_ARCH_ARM) && defined(__GNUC__))


// MSVC Intrinsics
// Used on MSVC on all archs, plus used by Clang on Windows on x86

#if KMP_ARCH_AARCH64 && KMP_COMPILER_MSVC && !KMP_COMPILER_CLANG

// MSVC/AArch64 specific bits

#else // !KMP_ARCH_AARCH64

// MSVC/X86 specifics

#endif


#elif (KMP_ASM_INTRINS && KMP_OS_UNIX) || !(KMP_ARCH_X86 || KMP_ARCH_X86_64)

// GCC Intrinsics, __sync_*, __atomic_*

#else

// Relying on external function definitions

#endif

Clang hasn't implemented the full set of MSVC intrinsics for atomics, so for Windows on non-x86, Clang is better off with the GCC style intrinsics of __sync_* and __atomic_*. D137168 / a356782426f5bf54a00570e1f925345e5fda7b2e added && !(KMP_ARCH_AARCH64 && defined(__GNUC__)) to the first condition, to single out the aarch64+mingw condition, but the same issue (Clang doesn't handle the full set of MSVC aarch64 atomic intrinsics) is present in Clang in MSVC/clang-cl mode too. (D138689 / 97958c9bb83cec44b6ce13e732b53de0171a5d43 then added ARM to the same condition.)

[DavidSpickett]

LGTM, thanks for explaining.

openmp/runtime/src/kmp_os.h

enum kmp_mem_fence_type {
   kmp_no_fence, /* No memory fence */
   kmp_acquire_fence, /* Acquire (read) memory fence */
   kmp_release_fence, /* Release (write) memory fence */
   kmp_full_fence /* Full (read+write) memory fence */
 };
 
 // Synchronization primitives
 
-#if KMP_ASM_INTRINS && KMP_OS_WINDOWS && !((KMP_ARCH_AARCH64 || KMP_ARCH_ARM) && defined(__GNUC__))
+#if KMP_ASM_INTRINS && KMP_OS_WINDOWS && !((KMP_ARCH_AARCH64 || KMP_ARCH_ARM) && (KMP_COMPILER_CLANG || KMP_COMPILER_GCC))
 
 #if KMP_MSVC_COMPAT && !KMP_COMPILER_CLANG
 #pragma intrinsic(InterlockedExchangeAdd)
 #pragma intrinsic(InterlockedCompareExchange)
 #pragma intrinsic(InterlockedExchange)
 #if !(KMP_COMPILER_ICX && KMP_32_BIT_ARCH)
 #pragma intrinsic(InterlockedExchange64)
 #endif